Choosing to protect a particular rate and program for a specific period of time.
Rates and costs change daily (sometimes more often). You may select a rate at a given cost at any time during the loan process, from before your application to when your transaction is submitted to the title company for sign-off. This is called locking your rate. Once locked, the lender cannot change the rate, and neither can you.
"Locking in" a rate means that the lender guarantees you will get the rate being advertised if your loan is approved within the lock-in period. Rates may be locked in at the time of application, at the time of loan approval, or at the time of settlement.